This invention relates to a multianalyte test vehicle which may be used in diagnostics and monitoring particularly optical immunodiagnostics.
In the fields of diagnosis and monitoring e.g. patient health care, there have been two main approaches to the analysis of samples from patients The first approach is concerned with a generally qualitative evaluation of whether an analyte is present or whether the level of analyte in a test sample deviates from acceptable limits while the second approach is concerned with the quantitative evaluation of the amount of analyte in a sample.
Usually the diagnostic devices used in the first approach are relatively inexpensive and disposable. An example of such a device is the so-called dipstick device used to test for glucose in the urine of diabetics. The dipstick device comprises a test area which is usually loaded with several enzymes and a chromogen. In the example of testing for the presence of glucose, a liquid sample, usually urine, is applied to the test area and results in a colour change of the test area in only a few seconds. The colour change after a given time is broadly divided into three categories which are discernable by the naked eye in comparison with a colour chart, viz. normal, glucose present but below a certain concentration, and glucose present in unacceptable concentrations. It is relatively easy to see if a sample falls squarely within any one of the categories but it is difficult to decide on borderline samples especially as the sensitivity of such devices are seriously affected by their storage conditions (temperature, humidity etc). Nevertheless such devices are useful as they can give a qualitative answer with respect to a sample, their simplicity allows for their use by a person suffering from a chronic disorder or someone monitoring the presence of a particular substance and their inexpensiveness allows for their regular use. However, in many fields there is a need to make a quantitative assessment of the levels of analyte or different analytes in a sample.
In the past quantitative tests were performed individually by a skilled technician working in a laboratory under carefully controlled conditions. The high level of labour involved in effecting such tests made them very expensive; consequently attempts have been made to automate or partially automate these tests.
Many attempts at providing a multianalyte test apparatus have relied on metered sub-division of a sample into a number of aliquots; each aliquot being tested for a different analyte. Expensive pumping equipment and complicated purging systems were needed in these apparatus to control the consistent division of the sample and to avoid problems of contamination caused by earlier samples. The cost and complexity of this sort of apparatus has meant that it is usually located at hospitals, if concerned with medical samples, or central laboratories removed from the site where monitoring is needed e.g. when monitoring a food production line or river for contamination. The remoteness of the apparatus from the place where the sample is taken causes a delay in effecting the test and obtaining a result. Sometimes the delay is unacceptable. Thus there is a general need to provide a multianalyte test apparatus which avoids the disadvantages associated with prior art apparatus and which has some of the elements of simplicity and ease of use associated with disposable diagnostic devices.
Much work has been done in the field of optical biosensors in an effort to simplify multianalyte test apparatus. An optical biosensor is a small device which, together with its measuring instrument, uses optical principles quantitatively to convert chemical or biochemical concentrations or activities of interest into electrical signals. The sensor may incorporate biological molecules, such as antibodies or enzymes to provide a transducing element giving the desired specificity. The range of application of such sensors is vast although many requirements, such as working temperature range, sterilizability or biocompatibility, have limited range.
Recently, an optical biosensor for immunoassays, the fluorescence capillary-fill device (FCFD) has been proposed. The device is based on an adaptation of the technology used to mass manufacture liquid-crystal display (LCD) cells. The device uses the principles of optical fibres and waveguides to reduce the need for operator attention and it avoids the need for physical separation methods or washing steps in the assay. An FCFD cell typically comprises two pieces of glass which are separated by a narrow gap. One piece of glass is coated with a ligand and acts as a waveguide. The other piece is coated with a dissoluble fluorescent reagent which has affinity for the ligand (in competition assays) or the analyte (in non-competitive labelling assays). When a sample is presented to one end of the FCFD cell it is drawn into the gap by capillary action and dissolves the reagent. In a competitive assay the reagent and analyte compete to bind to the ligand on the waveguide and the amount of bound reagent is inversely proportional to the concentration of analyte. In an immunometric assay, the amount of reagent which becomes bound to the waveguide is directly proportional to the amount of analyte in the sample. As the gap between the pieces of glass is narrow (typically 0.1 mm) the reaction will usually go to completion in a short time, probably in less than 5 minutes in the case of a competition assay.
FCFD cells avoid the need for separation steps and/or washing steps by using an optical phenomenon known as evanescent wave coupling. Basically, the fluorescence from unbound reagent molecules in solution enters the waveguide which comprises the baseplate of the FCFD at relatively large angles (e.g. more than 44.degree. for a serum sample) relative to the plane of the waveguide and emerge from the waveguide at the same large angles in accordance with Snell's Law of Refraction. On the other hand, reagent molecules bound to the surface of the waveguide emit light into all angles within the waveguide. By measuring the intensity of fluorescence at smaller angles to the axis of the guide (e.g. less than 44.degree. for a serum sample), it is possible to assess the quantity of reagent bound to the surface thereby allowing the amount of analyte in the sample to be measured. The principles involved in FCFDs are described in more detail in U.S. Pat. No. 4,978,503.
As mentioned earlier the ligand bound to the waveguide is selected to suit the FCFD to a particular assay. Also, FCFDs allow for rapid tests without the need for accurate measurement of sample or reagent(s) and without the need for separation and washing steps. These factors suggest that FCFDs will be useful in simplifying multianalyte test apparatus. However, there is a need to provide an arrangement whereby the timing of the contact of sample with the FCFDs is controlled, since timing is important in rapid assays, and where the various FCFDs can be brought into alignment with both the light source acting as the fluorescence pump and the fluorescence detector which needs to be aligned with the end of the waveguide. Moreover, there is a need to avoid contamination of the optical surfaces of the FCFDs by stray sample or other matter which would affect optical quality.